Fix 6398209: SearchPanel gesture improvements

This fixes a few recent regressions caused by other bug fixes:
- add new flags to animateCollapse() so we can selectively close panels. Fixes regression caused by attempt to close recent apps from startAssistActivity() which had the side effect of closing the search panel before the animation completes.
- adds tuneable holdoff delay for responding to home key press.
- minor tweaks to MultiWaveView animations.

Change-Id: Ia48434b8d59e7b0290a5e9783960c2f684068218